Apparatus for aerogravimetric prospecting



Jan. 27, 1953 Filed July 8, 1946 c. A.-HE|LAND 2,626,525

APPARATUS FOR AEROGRAVIMETRIC PROSPECTING 3 Sheets-Sheet l INVENTOR.

Carl .A. Heilond Jam 7, 1953 c. A. HEILAND 2,626,525

APPARATUS FOR AEROGRAVIMETRIC PROSPECTING Filed July 8', 1946 s Sheets-Sheet 2 INVENTOR. Carl A. Heilund Jan; 27, .1953.

Filed July 8, 1946 C. A. HEILAND APPARATUS FOR AEROGRAVIMETRIC PROSPECTING 3 Sheets-Stfeet 3 INVENTOR. Carl A- Heilond Attornevs Patented Jan. 27, 1953 UNITED APPARATUS FOR AEROGRAVI'METRIC PRO SPEQTING Carl A. Heiland, Denver, Colo. Application July s, 1946, Serial No. 681,907

4 Claims. (Cl. 73-'-382) This invention relates to improvements in-apparatus for locating potential oil bearing structures in the earths geologic formations by the 'use of gravimetric devices lowered to the ground "from certain types of aircraft. By this type'of prospecting} the investigation of large areas may be carried on rapidly regardless of the character of vthe surface topography and the existence of gravitational anomalies may be detected inregions which would otherwise be inaccessible, such as swamps, jungles and the like.

It is well 'known to those versed in the art "that the occurrence of oil deposits in the earth is controlled by the existence of suitable traps in subsurface geologic structures. These traps include faults, anticlines, domes and salt'plugs.

"In allof these structures oil bearing strata,- which were-laid down originally in horizontal-positions, "have been uplifted or tilted, making possible a 'densityseparation of gas and oil and a separation of the oil from the so-called connate waters contained in the oil beds. Oil deposits may therefore be located indirectly by prospecting for the types of geologic structures just mentioned. Experience has shown'th'at oil bearing structures, particularly those associated with uplifts, generally produce gravitational anomalies. Due tothe fact'that in the core of an uplift, the older and usually denser strata are brought closer to the surface, the presence of anticlines and domes generally will be indicated by gravitational highs,

that is, by local increases in the force of gravity. exception to this rule are salt plugs which, because of. the fact that salt is lighter than the surrounding sediments; are usuallyindicated by 3 5 gravitational lows. v

- I Gravimetric prospecting for oil bearing structures has in the past been mostly confined to land area's and the like which are' generally ac- "cessible to vehicle transport; Another'complica jgrav'imetric surveys of inaccessible areas may "be '*made through the use of aircraft for carrying a "gravimeter to such 'areas, coupled with means for determining accurately the elevations of the "points at which measurements are made. More IP t ese, it ts are accomplished lowering a gravimeter to thedesired places on the earths surfac from aircraft such as a helicopter "or'a dirigible balloon, either of which is capable of slow movement and of hovering over agiven "point, making gravity measurements at those places, and determining by optical or. radio' triangulation methods the relative elevations, of the places where gravitymeasurementsare made. Otherobjects' relate to various features of the apparatus which will appear more fully hereinafter.

The nature of the invention will be understood from the following specification taken with the "aceompanying'drawin'gs in. which one embodiment of the improved. apparatus and certain modifications thereof are disclosed in connec- .Fig. 2 shows an enlarged vertical section I through the principal part of the gravity mea s uring device illustrated in Fig. 1; V

Fig. 3 shows, a horizontal section on the line 3-3 Of Fig. 2; v

Fig. 4 shows a-horizontal sectionon theline .4-4 of Fig. 2; I M

Fig. 5 shows an enlarged detail of the circuit connections of a portion of th apparatus illusrat lin' e. 2;. V 2 "v Fig; 6 illustrates in perspective an opticalt riangulation method which may be employed to determine the elevation of the ,gravimeter station;and 1 Figs. 7 and 8 illustrate somewhat diagrammatically a radio location method which may be used to find the elevation ofth e gravimeter station. I The aircraft ,used in-this work maybe a heli- 1, copter plane or-a dirigible balloonv oi the type commonly known as -a blimp by which the gravimetric instrument is carried to the desired ;:loc,ation and from which this instrument-is then ilowered to the ground by means; of a cable.-;-In Fig. '1. a, helicopter I0 is shown hovering in a substantially. stationary position over .av place on the surface of the .earth "Hi: to which a gravimetric measuring device IZfsuSpended from I a skeleton-like tripod or frame l4, ha's been 10wer'ed from'the airplane bymeans of a ca'ble I5. The frame l4 and the measuring" instrument l2,

observer.

"shaped-top bracket 22a of the frame.

suspended therein by a wire or the like It, are of sufficient weight to cause the spikes I5 carried by the frame to enter the earth and hold the frame in a fixed position. The cable I5 is payed out from a winch on the helicopter or other aircraft employed and the gravimeter and its tripod or frame serve as an anchor to hold the aircraft temporarily above thespot where the measurements are to be made.

Although the gravimetric measuring instrument I2 levels itself with a substantial degree of accuracy by virtue of its suspension by the wire I6, means are provided, as shownin Figs. 2, 3 and 4, for more accurately leveling the measuring mechanism inside of the casing in which it is housed and means are also provided for obtaining a dial reading of the gravity measurement while the instrument is on the ground so that, when the instrument is subsequently hoisted back onto the aircraft, that reading may be taken off by the There is provided within the outer casing IT, to which-the wire I6 is attached, a heavy supporting plate I8 from which the reengagements with nuts 20 secured in the plate I8. The lower ends of the screws I9 are mounted in ball bearing units '2I which are mounted on the top wall 22a of a frame 22 on which the measuring instruments proper are located. The

screws I9 are located opposite to each other in right-angularly disposed pairs'so that by their "adjustment the frame 22 may be tilted in any desired fashion to effect .a proper and accurate leveling of the-gravity measuring mechanism.

For the purpose of turning the screws I9 they are each provided with a relatively fixed 'bevel gear 24 which meshes with a bevel pinion 25 fixed on a shaft 26 of one of the radially extending-pairs of shafts 26 and 21., each of which is journalled ina bearing 28 carried by thecross- The pair of aligning shafts 29 are connected by universal joints 29with an intermediate shaft30 j'ournalled 'in a block -3I carried bythe top bracket22a-and having fixed thereon a worm wheel 32. This wormwheehmeshes'witha worm 35 fixedupon the upper end of a shaft 36 which is driven in the' m'anner hereinafter described to effect the tilting or leveling of the frame 22-andits con- "tents in: the-plane of the screws I-9 'to"'whi'chthe "ShaftsZB-are connected. The shafts 21, which are located in a plane at right angles to the plane containing the shafts '26, have fixed thereon 'a worm wheel 38 arrangedto mesh with a worm -39 fixed on the upper end of a shaft 40 adapted to be driven in the manner hereinafter described. The operation of the shaft 40 will thus tilt the frame 22 and its contents in the plane of the connect the outer edges of the brackets 22a and -22b and which are in turn connected by four radiating intermediate arms 22d united with each other at their inner ends, forming a hub 222a.

This hub is supported from the bottom bracket- 221) by a center post 22f.

Beneath each-of two right-angularly disposed arms 22d of theframe' 22 there is mounted a horizontal pendulum M as shown in Figs. 2 and 4. Each pendulum comprises a vertical shaft 4 Ia having cone-shaped extremities, the lower one of which has a bearing in a block 42 mounted in the bottom plate 22b while the upper extremity has a bearing in a recess in the under side of a bearing block 44 mounted in the hub portion 22c and adjustable by means of a screw 44a for the purpose of regulating the position of the pendulum. Each pendulum is provided at its outer end with a bob 4Ib from the outer extremity of which a damping vane 45 of copper or the like extends between the poles of a permanent magnet 46 by which the swinging movements of the pendulum are damped.

The upper portion of the shaft 4Ia of each horizontal pendulum has mounted thereon a mirror 41 adapted to receive a narrow beam of light 48 from a Lucite tube 49 extending from an alternating current or interrupted current light source 5Il. The beam of light 48 received by-each mirror 41 is reflected alongthe path '51 to a V- shaped prism 52 (see Fig. "5), mountedon one of thelegs 220, which splits the 'beam'and directs the light to two photo-electric cells '54 and 55 mounted at opposite sides "of the prism on the adjacent leg 220. The double-faced prism'a'n'd the two photo-electric cells are so arranged and adjusted that when the reflected light beam strikes the prism evenly so'that the same amount of light strikes each photo-electric cell, the instrument is exactly level in a plane'at right angles to the arm 22d beneath which the associated horizontal pendulum M is mounted. The circuit connections of each pair of photo-electric cells .54 and 55 in relation to the light beam and the ad- -jacent prism are shown in Fig. 5 where the termi- -justing screws I9 and the other servo-motor 58 is connected to drive the vertical shaft 40 by which the other pair of adjusting screws I9 are operated. In this way a movement of the measuring instrument in either of two right-angularly disposed directions out of a true level position will cause a swinging of one of the horizontal pendulums 4I out of its centeredposition and a resulting actuation of the related photo-electric cells 54 and 55 to cause one of the servo-motors 58 or 59 to operate two-of the adjusting screws and restore the level condition in that direction.

Under another of the arms 22d of the frame22 there is pivotally mounted a vertically swinging pendulumtfl which is provided at its inner end with a pointed extremity 60a adapted to rock in a recess formed in a Web 229 of the frame which extends vertically betweenthe adjacent arm 22d and the bottomplate 22b. This pendulum has a bob 60b at its free end and a coil sprin 6| extends between a point on the pendulumadjacent the bob to the upper end of the web 22g, making an angle of approximately forty-five degrees with the longitudinal axis of the pendulum. At its inner end thependulumBU carries an-upstanding arm 600 on which is mounted a mirror 62 adapted tto ,receive a small beam of light 64 from a Lucite tube 65 leading from the previously described light source 50. The' beam of light-64 is reflected from the mirror 62 along a line 6B to a double prism 61 mounted on one of the legs 220 with its apex extending horizontally. Two photo- .electriccells 68 and B9 are mounted on opposite sides of the prism 61, one above and'o ne belo'w,

and when the pendulum 60 is in the zero or ref- ..erence position, which may be termed its minimum level sensitivity position, the beam-of light is divided into equal parts by the prism 61 and equal amounts of light pass to the photo-electric cells 68 and 69. 3

After the gravity measuring instrument has been leveled by the action of the adjusting screws [9 in the manner previously described, the pendulum 60 will usually be out of the zero'or reference position just referred to and the major portion of the light in the beam will pass to one or the other of the photo-electriccellsfiil or 69. These cells are connected in circuit with an amplifier and a servo-motorlll, shown inlFig'; in the manner "previouslydescribedin connection with Fig.5, so that when this unbalanced condition exists between the cells 68 and 69, the connected amplifier causes the servo-motor 10 to operate and thereby actuate a pinion H through a, mechanical connection 12, illustrated diagrammatically in Fig. 4, and this pinion drives the meshing gear l4 having a threaded engagement with a micrometer screw 15. This micrometer screw thus moves endwise under the influence of the servomotor 1e and through suitable mechanism, illustrated for convenience as a spring 16, the pendulum 6B is moved back to its zero or reference position. The extent of this movement is an indication of the force of gravity at the place where the instrument is located and may be recorded on a dial or counter. For example, the micrometer screw 15 may be connected to a flexible shaft H which will actuate a counter 18 located on the outside of the housing II. By the use of this mechanism the gravity measurement at each station will require only a short period of time, whereupon the instrument I2 and its frame or tripod M are hoisted back onto the aircraft l and the dial position is noted and recorded.

This reading of the relative value of gravity at a station would be without value unless means were provided for determining accurately the elevation of the station. It is assumed that surveyors cannot get to the station and other means must therefore be employed to find the station elevation. One method, which is accurate. although somewhat complicated, is illustrated in Fig. 6. According to that plan, the position of the aircraft in space is determined at all times by recording telescopes Tl, T2 and T3 set up at three ground stations which are removed from the inaccessible location where the gravity measurement is taken. Two of these telescopes TI and T2 are suflicient but the third one is convenient when unfavorable angles are encountered. Through the use of these telescopes there are obtained, at any instant, the values of the angles al, a2 and a3, thus fixing the horizontal position of the aircraft to with respect to the three stations, and also the angles bl, b2 and b3 which fix the vertical elevation h of the I aircraft above a plane containing the three stations. By recording the times on the ground when these simultaneous observations are made and by making concurrent time determinations in the airplane Iii, the position of the airplane in space, particularly its vertical elevation above the ground, is determined. To arrive at the elevation of the station where the instrument I2 is located when a measurement is taken, it is merely necessary for the observer to read graduations provided on the hoisting cable l to determine directly the elevation of the aircraft above that measurement station.

Ales's a'ccuratebut more rapid method ofd'etermining the elevation is shown inFigs. 7 and 8, where the airplane to isequipped with two short wave radio transmitters T1" which trigger two (or more) radio ground stations with receivers RI and R2 and transmitters Tri andTrZ which .are spaced apart a distance D. The impulses transmitted by the two ground stations TM. and T11 are received in the plane by'the receivers R. For purposes of identification and ease of operation the frequencies of the two channels are different. .The distance of the aircraft from the two stations RI' and R2 may be indicated by the --periodsoftimetl and t2 required for the impulses to travel from the aircraft to the receivers R! and R2 and return; which, may be indicated by dials SI and S2 in. a conventional manner. The location of the airplane with respect to the two ground stations is thereby established approximately since ti and t2 are proportional to the horizontal distances di and d2, respectively. The absolute elevation of the aircraft above sea level is then determined by using a microbarometer; and the elevation hl of the plane above the measuring station M may be detertnined by using the hoisting cable as a measuring ape.

Through the determination of the relative elevations of the measuring stations and the measurement of the force of gravity at those stations which may be distributed as desired over a large area, some parts or all of which may be inaccessible to land transport, it is possible to obtain an indication of the presence or absence of potential oil bearing structures in the underlying geologic formations.

Although one embodiment of the improved gravimetric apparatus has been shown and described and modifications of certain portions thereof, by way of illustration, it will be understood that the apparatus may take various forms within the scope of the appended claims.

I claim:

1. In apparatus for gravimetric surveying from aircraft, a gravity measuring device adapted to be lowered to the ground from said aircraft and comprising a ground engaging frame having a supporting plate, a gravity measuring instrument suspended from said plate by leveling means, and means comprising two horizontal pendulums normally located in right-angularly disposed planes for automatically operating said leveling means to level said instrument in two directions.

2. In apparatus for gravimetric surveying from aircraft, a gravity measuring device adapted to be lowered to the ground and including a ground engaging frame, a gravity measuring instrument suspended from said frame by leveling means, and means comprising servomechanism actuated by two horizontal pendulums normally located in right angularly disposed planes for automatically operating said leveling means to level said instrument in two directions.

3. In apparatus for gravimetric surveying from aircraft, a gravity measuring device adapted to be lowered to the ground and including a ground engaging frame, a gravity measuring instrument suspended from said frame by leveling means, and means comprising servomechanism actuated by two horizontal pendulums normally located in right angularly disposed planes for automatically operating said leveling means to level said instrument in two directions, said gravity measuring instrument comprising means for automatically recording the gravity measurement while said device is supported on the ground.

4. In apparatus for gravimetric surveying from aircraft, a gravity measuring device adapted to be lowered to the ground and comprising a ground engaging frame, and a gravity measuring instrument suspended from said frame by automatic leveling means, said instrument comprising a vertically swinging pendulum for causing a light beam deflection and photoelectrically actuated means for correcting the beam deflection and recording the gravity measurement indicated thereby within the instrument while said Number instrument is so supported on theground.

CARL A. I-IEILAND.

REFERENCES CIT-ED UNITED STATES PATENTS Number Name Date 2,190,959 Bornemisza Feb. 20, 1940 2,253,472 Pepper Aug. 19, 194-1 2,358,103 Ryder Sept. 12, 1944 2,362,135 James Nov. 7, 1944 2,383,966 Hasbrook Sept. 4, 1945 2,384,739 Hasbrook Sept. '11, 1945 FOREIGN PATENTS Country Date 586,909 Germany v Jan. 26, 1933 

